Piezoelectric oscillator



Sept. 3, 1946. H. BENIOFF PIEZOELECTRIC OSCILLATOR Filed July 8, 1940 2Sheets-Sheet 1 INVENTOR.

HZ/fd Ben/off W may Sept. 3, 1946. H. BENIOFF I PIEZOELECTRIC OSCILLATORFiled July 8, 1940 2 Sheets-Sheet 2 l WI INVENTOR. Hygo Benioff' mimPatented Sept. 3, 1946 PIEZOELECTRIC OSCILLATOR Hugo Benioif, La Canada,-Calif., assignor, by

mesne assignments, to Submarine Signal Company, Boston, Mass acorporation of Delaware Application July '8, 1940, Serial No. 344,363

tal of the Rochelle salt or other similar type.

The principles of the present invention may be applied either toa unitofa small radiating surface, in which case the vibrator tends to benondirectional or to a vibrator which has large linear dimensions incomparison to the wave length to be transmitted. in the propagatingmedium which may be air or water, but preferably water, to which thepresent invention is readily adapted.

In the present invention the piezoelectric oscillatoris so arrangedthatit is vibrated or vibrates longitudinally in response to theapplication of oscillating or varying electrical potential acrossopposite faces of the crystal perpendicularl to thelongitudinalvibrations. The crystal as a longitudinal vibrator is made to vibrate bycompressional wave forces exerted at the crystal ends which act to varythe crystal length. Further, in order to eliminate spurious modes ofvibrations it is desirable that the frequency of the lowest longitudinalmode of the crystal be higher than the operating frequency of theoscillatory structure in which it is mounted.

In the present invention the crystals maybe arranged in triangular,rectangular, hexangular or other group patterns and these units, eachcomprising a single longitudinal vibratory structure, may'be .nestedtogether on a plate which is designed so that the mass of the plateassociated with each structure produces the desired sharpness ofresonance. As the groups aredistributed over the whole surface of theplate, the radiating face of the plate is vibrated in unison over itswhole surface even though the plate is not inherently still enoughitself to act as a piston.

The merits and advantages of the present invention will be more fullylearned and understood from the description in this specification of anembodiment of the same described in connection with the drawings inwhich Fig. 1 shows a sectional elevation through the center of thedevice taken on the line l-| of Fig. 2; Fig. 2 shows a plan view as seenfrom the top of Fig. 1 with the back casing removed; Fig. 3 shows aperspective View of one of the units of Figs. 1 and 2; Fig. 4 shows adetailed section taken on the line 4-4 of Fig. 2; Fig. 5 shows anelevation of a single unites viewed in the direction of the arrow'5 ofFig. 2; Fig. 6 shows a perspective View corresponding to Fig. 3 of arectangular unit; and Fig. 7 shows in section a further modification.

.In .Figs. 1 and 2 there is a plurality of units 8, 43, 8, etc., mountedin hexagonal fashion on a heavy plate 9 the opposite side of which maybe in'contact with water and serve as the radiating surface providingthereby a proper seal so 18 Claims. (01. 1-77386) that the vibratingelements operate in air. plate 9 is supported through a thin flange IE1and a heavy periphery ring ll to thecasing 12 by means of a series ofbolts is spaced around the flange. A gasket ll between the flange ii andThe casing makes the casing watertight. The units 8 are nested togetherin a hexagonal pattern in such a way as to substantially cover the plate9 which itself is hexagonal in shape. For other forms of platesdifferent nestings andarrangements of units may be employed and therectangular unit shown in Fig. 6, for instance, willcover a rectangularplate surface more completel than the unit of Fig. 3. The unit 8, whichmay be made from a solid piece of material, has a triangular centersection Hl with flat faces it which may have a plurality of outwardlyprojecting ribs which keep the piezoelectric crystal it from restingagainst the wall surface I4 and thereby reducing frictional forcesbetween the crystal and thi surface. At the ends of the triangularsection Hi there are provided mass sections l1 and 8, each havingoutwardly extending flanges. The elements IT. and [8 are preferably ofsubstantially the same shape as the triangular section Hi, This mannerof construction of the unit 8 permits the mounting of threepiezoelectric crystals one against each face Id of the triangularsection. These crystals it are cemented against the ribs l 5 and to thesurfaces of the end bearing projecting flanges in such a way that theyare firmly fixed to the metallic structure so that no play can existbetween the flange and the ends of the crystal. These crystals are socut that changes in length brought about by varying pressures appliedlengthwise of the crystals at their upper and lower ends will set upelectrical variations in potential between the electrodes I9 and 28mounted on opposite crystal faces.

Each unit is supported to the plate in the manner indicated in Fig. 4. Ahole 2i is bored through the center of the unit and at the lower end isprovided with a shoulder 22 against which the head of the screw 23 bearsas it is screwed into the plate .24. It is also essential to cement theunit to the plate between the contacting urfaces at 25 as it isessential to provide a continuous acoustic path to make the plate .24 apart of the longitudinal vibratory acoustic structure.

Other methods of coupling the unit 8 to the plate may be employed as,for instance, a fluid coupling of some plastic or viscous material.However, the method indicated here has proved to be preferable in thisconstruction.

The crystals mounted in each unit may be connected in parallel or seriesparallel by proper insulation of the crystal electrodes. In this casethe electrodes l9 on the outside surfaces of the unit may be allconnected together by a band 26 which is connected to a terminalconnector 21 the inner faces of the crystals. The electrodes may also beextended to form leads.

In the unit shown in Fig. 6 the structure is quite similar to that inFig. 3 with the exception that the unit provides only two crystals 30and 3!, one on each of two opposite faces of the unit. The unit 32 ofFig. 6 is provided with end masses 33 and 34 which have projectingflanges 35 hanging over and bearing upon the ends of the crystals. Inthe operation of the device the metallic structure of the unit 3 withits base portion as, for instance, the section indicated by 24 in. Fig.4, forms a longitudinal vibratory structure at a definite resonantfrequency.

The nodal point may either be between the lines A and B, referring toFig. 4, or the nodal point may be outside of this section although wherethe units are attached to a large diaphragm or plate in order to preventtransverse vibrations in the plate, it is for the most part desirable tohave the nodal point outside or practically outside of the large plate.

In order to reduce spurious vibration modes at high frequencies thecrystal [6 is cemented at its ends to the metallic flanges and thenatural crystal frequency is chosen to have a longitudinal resonancewell above that of the resonance of the metallic vibratory structure.Since, however, the crystal itself is firmly united with the metallicelement to form a single unitary structure, the unit when assembled hasonly a single resonant point, which is close to the resonance of themetallic system.

In the operation of the oscillator when the plate 9 is vibrated at theproper resonant frefrequency for the system, longitudinal vibration isset up in the unit 8, compressing and expanding the crystals E by actionat their ends whereby the crystals !6 expand and follow the motion ofthe surfaces A and B. The end surfaces of the crystal will always keepin contact with the surfaces of the metal. When the metallic unitisvibrated, electrical potentials are set up across the electrodes l9and 20; and conversely when electrical potentials are set up across theelectrodes as when the device is used for transmitting compressionalwaves, the ends of the crystals exert pressure against the metallicsurfaces A and B and produce longitudinal vibrations of the unit 8 inthe plate 9.

In Fig. 7 a unit is shown in which the lower bearing surface for thecrystals 49 and M is furnished by the plate 42 of the radiating memberagainst which the crystals are cemented. The mechanical unit 43, whichwith the plate 42 is designed to form a resonant structure at thedesired frequency, is held to the plate in the same way as explainedabove by means of the screw 44 which is screwed into the plate.

Having now described my invention, I claim:

1. A piezoelectric oscillator adapted to be used for transmitting andreceiving compressional waves comprising a resonant longitudinallyvibratory element having a recess with the shoulders of the recess atopposite sides of a node in the longitudinal system, a piezoelectriccrystal having its ends cemented to said shoulders, said crystal havingits mechanical axis parallel to the plane of longitudinal vibration andits electric axis transverse thereto.

2. A piezoelectric oscillator adapted to be used for transmitting andreceiving compressional waves comprising a resonant longitudinallyvibratory element having a recess with the shoulders of the recess atopposit sides of a node in the longitudinal system, a piezoelectriccrystal having its ends cemented to said shoulders, said crystal havingits mechanical axis parallel to the plane of longitudinal vibration andits electric axis transverse thereto, said crystal having a natural freeresonance above that of the longitudinal vibratory unit.

3. A piezoelectric oscillator adapted to be used for transmitting andreceiving compressional waves comprising a resonant longitudinallyvibratory member formed with two end masses substantially greater thanthe portion of the member between the ends, a piezoelectric crystalmounted upon said member with its ends bearing upon said masses, thecomposite longitudinally vibratory structure so formed having a nodebetween said end masses and having a resonant frequency substantiallylower than that of the free resonant frequency of the piezoelectriccrystal by itself.

e. A piezoelectric oscillator adapted to be used for transmitting andreceiving compressional waves comprising a resonant longitudinallyvibratable metallic structure having a central element with elementsformed at each end providing heavier masses than the central element,said metallic structure having a node in said central element at theresonant frequency, said end masses forming parallel bearing surfaces, apiezoelectric crystal mounted between said bearing surfaces, saidcrystal being adapted to produce electrical variations betweenelectrodes positioned in a plane substantially normal to the planes ofsaid bearing surfaces.

5. In a piezoelectric compressional wave oscillator, an oscillator unitcomprising a plurality of piezoelectric crystals, a longitudinalstructure having a substantially rectangular sectional shape with aplurality of mounting surfaces forming the faces of said rectangle, saidunit having flanges extending at each end of the crystal, saidpiezoelectric crystals each mounted on one of said faces, said crystalshaving their ends and side cemented respectively to the said flangesurfaces and faces whereby longitudinal vibration of 50 said structurewill produce corresponding vibrations in said crystals.

6. In a piezoelectric compressional'wave oscillator, an oscillator unitcomprising a longitudinally vibrating resonant metallic system having a55 central longitudinal member connected to end masses providingopposing surfaces substantially normal to the longitudinal direction anda piezoelectric crystal mounted securely against said opposing surfaces.

7. In a piezoelectric compressional Wave oscillator, an oscillator unitcomprising a resonant longitudinally vibrating metallic system having acentral longitudinal member connected by end masses providing opposingsurfaces substan- 65 tially normal to the longitudinal direction, a

plurality of piezoelectric crystals mounted securely against saidopposing surfaces and having their compressional axes substantiallyparallel to the longitudina1 axis of the metallic vibratory 70 system.

8. In a piezoelectric compressional wave oscillator, an oscillator unitcomprising a resonant longitudinally vibrating metallic elementsymmetrically constructed with respect to the cen- 75 trallongitudinalaxis, said element having'end 'of said element;

10. In a piezoelectric compressional wave oscillator, an oscillator unitcomprising a resonant longitudinally vibrating metallic element, saidelement having end masses providing flange surfaces opposite one anotherextending around said metallic element, and a plurality of piezoelectriccrystals mounted between said opposite surfaces around said element withtheir compressional axes substantially parallel to the longitudinal axisof said element, said longitudinal vibratory structure providingmounting supports against which the piezoelectric crystals rest.

11. In a piezoelectric compressional wave oscillator, an oscillator unitcomprising a resonant longitudinally vibrating metallic element, saidstructure having end masses providing flange surfaces opposite oneanother extending around said metallic element, and a plurality ofpiezoelectric crystals mounted with their compressional axessubstantially parallel to the longitudinal axis of said element andbetween said opposite surfaces around said element, the portion of saidelement between said end masses providing surfaces parallel to thelongitudinal axis of the element, said surfaces having a plurality ofprojecting ribs against which said piezoelectric crystals rest.

12. In a piezoelectric compressional wave oscillator, an oscillator unitcomprising a resonant longitudinally vibrating metallic element, saidstructure having end masses providing flange surfaces opposite oneanother extending around said metallic structure, and a plurality ofpiezoelectric crystals mounted with their compressional axessubstantially parallel to the longitudinal axes between said oppositesurfaces about said structure, said structure being triangular in shapeand providing three surfaces extending parallel to the longitudinalaxis, said surfaces having projecting ribs against which said crystalsare mounted.

13. A piezoelectric compressional wave oscillator comprising a platehaving a thin supporting web at the periphery thereof, a pluralit ofoscillator units each comprising a resonant longitudinally vibratingmetallic element having end masses extending normally from the centralportion of said vibratory element and providing opposed surfaces aboutthe central portion of the vibratory element, a plurality ofpiezoelectric crystals cemented securely against said opposing surfacesand means acting through the axis of said longitudinal vibratory elementsecurely holding said element to said plate, said plate and saidoscillator unit combining to form each a resonant longitudinalvibratable structure with a node between the radiating surface and rearsurface of the oscillator unit.

14. A piezoelectric compressional wave oscillator comprising a platehaving a thin supporting web at the periphery thereof, a plurality ofvibrator units each comprising a resonant longitudinally vibratingmetallic element having end masses extending normally from the centralportion of said vibratory element and providing 0pposed surfaces aboutthe central portion of the vibratory element, a plurality ofpiezoelectric crystals mounted securely against said opposing surfaces,said vibrator unit having a bore extending through the center of saidunit along the longitudinal axis, means acting in said bore to clamp theunit to said plate and means cement ing together the clamping surfacesbetween the plate and said vibrator unit, said plate and said vibratorunit combining to form each a resonant longitudinally vibratablestructure with the node between the radiating surface and the rearsurface of the vibrator unit.

15. A piezoelectric compressional wave oscillator comprising a platehaving a thin supporting web at the periphery thereof, a plurality ofoscillator units nested together over substantially the whole platesurface, means clamping said oscillator units directly to said plate andeach said unit forming with the section of plate adjoining the end aresonant longitudinally vibratory structure vibrating normal to thesurface of the plate, each of said vibratory units providing end masses,said masses having bearing surfaces for mounting a plurality ofpiezoelectric crystals for compressional vibration with the meianicalaxes parallel to said longitudinal axes.

16. An underwater compressional wave oscillator comprising a watertightcasing having one side formed as a plate the outer face of which isadapted to act as a radiating surface, a plurality of vibrating elementsmounted on the inner surface of said plate in close proximity to eachother and each comprising a polyhedral structure having a longitudinalaxis perpendicular to said plate and forming with a portion of saidplate a, resonant longitudinal vibrator, said polyhedral structurehaving a recess in one or more face thereof and piezoelectric crystalsmounted within said recesses with their ends cemented to the shouldersof said recesses and with their mechanical axes parallel to thelongitudinal axis of the structure.

17. A piezoelectric oscillator adapted to be used for transmission andreception comprising waves including a vibrator comprising a resonantlongitudinally vibratable element having recesses forming mass portionsat each end of said element and Rochelle salt piezoelectric crystalsmounted within said recesses and having their ends abutting andacoustically joined to the shoulders of aid recesses with the mechanicalaxes of the crystals parallel to the longitudinal direction of saidelement whereby the crystals and said element form a unitarylongitudinal vibrator having a natural fundamental resonant frequencywith a node between the ends of the vibrator.

18. In a piezoelectric compressional wave oscillator, an oscillator unitcomprising a resonant longitudinally vibrating metallic element havingrecesses in a plurality of its sides, a plurality of piezoelectriccrystals mounted between and securely against the shoulders of saidrecesses and having their compressional axes substantially parallel tothe longitudinal axis of the metallic vibratory element.

HUGO BENIOFF.

